Gas generant compositions

ABSTRACT

A novel compound, used for example, as a gas generating fuel, is defined as a compound having the structural formula of R 3 —R 1 —R 2 , wherein R1 is a benzene ring with nitro substitution, R2 is a tetrazolyl group with a C—C bond to the benzene ring, and R3 is a tetrazolyl group with a C—C bond to the benzene ring. A method of making the compound is also provided. A gas generating composition containing the novel compound as a fuel, and an oxidizer is also provided. The novel compound is contained within a gas generant composition, within a gas generator. The gas generator may be contained within a gas generating system such as an airbag inflator or seat belt assembly, or more broadly within a vehicle occupant protection system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 60/798,206 filed on May 5, 2006.

TECHNICAL FIELD

The present invention relates generally to gas generating systems, andto gas generating compositions employed in gas generator devices forautomotive restraint systems, for example.

BACKGROUND OF THE INVENTION

The present invention relates to gas generant compositions that uponcombustion produce a relatively smaller amount of solids and arelatively abundant amount of gas. It is an ongoing challenge to reducethe amount of solids and increase the amount of gas thereby decreasingthe filtration requirements for an inflator. As a result, the filter maybe either reduced in size or eliminated altogether thereby reducing theweight and/or size of the inflator. Additionally, reduction ofcombustion solids provides relatively greater amounts of gaseousproducts per gram or unit of gas generating composition. Accordingly,less gas generant is required when greater mols of gas are produced pergram of gas generant. The result is typically a smaller and lessexpensive inflator due to reduced manufacturing complexity.

Yet another concern is that the compositions must exhibit burn ratesthat are satisfactory with regard to use in vehicle occupant protectionsystems. In particular, compositions containing phase stabilizedammonium nitrate may exhibit relatively lower burn rates requiringvarious measures to improve the burn rate. Accordingly, the developmentof energetic fuels is one ongoing research emphasis whereby the lessaggressive burn characteristics of preferred oxidizers such as phasestabilized ammonium nitrate are accommodated and compensated.

SUMMARY OF THE INVENTION

The above-referenced concerns are resolved by gas generators or gasgenerating systems containing novel fuel constituents within novel gasgenerant compositions. Novel fuel constituents or compounds may bedefined as a molecule having the structural formula of R₃—R₁—R₂, whereinR1 is a benzene ring with nitro substitution, R2 is a tetrazolyl groupwith a C—C bond to the benzene ring, and R3 is a tetrazolyl group with aC—C bond to the benzene ring.

An optional second fuel may be selected from tetrazoles and saltsthereof, triazoles and salts thereof, azoles and salts thereof,guanidines and salts thereof, guanidine derivatives, amides, andmixtures thereof. An oxidizer is selected from metal and nonmetalnitrates, nitrites, chlorates, perchlorates, oxides, other knownoxidizers, and mixtures thereof.

In further accordance with the present invention, a gas generator or gasgenerating system, and a vehicle occupant protection systemincorporating the gas generant composition are also included.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional side view showing the general structure ofan inflator in accordance with the present invention.

FIG. 2 is a schematic representation of an exemplary vehicle occupantrestraint system containing a gas generant composition in accordancewith the present invention.

DETAILED DESCRIPTION OF THE INVENTION

A first aspect of the present invention provides a novel method offorming a nitrogen-containing compound, useful as a fuel within a gasgenerant system, for example. The method may be described by thefollowing steps:

-   -   1. Providing a sufficient amount of water within a reaction        vessel for full mixing/solubilizing, for mixing of the        ingredients described below. Then providing a predetermined        molar amount of a dicyano Nitrobenzene compound in the reaction        vessel and mix the contents.    -   2. Providing a molar amount of zinc bromide, equivalent to that        of dicyano Nitrobenzene, within the reaction vessel and        continuing to mix.    -   3. Providing, a molar amount of sodium azide, about two to three        times that of dicyano Nitrobenzene, to the reaction vessel and        continuing to mix.    -   4. Mixing the contents of the vessel, and refluxing the mixture        for about 36 hours.    -   5. The solution was cooled to room temperature, and acidified by        the addition of 3N hydrochloric acid to yield a white solid.    -   6. The final nitrogen-containing compound, as confirmed by IR        and DSC, may be defined as a molecule having the structural        formula of R₃—R₁—R₂, wherein R1 is a benzene ring with nitro        substitution, R2 is a tetrazolyl group with a C—C bond to the        benzene ring, and R3 is a tetrazolyl group with a C—C bond to        the benzene ring.

Reactions I and II as given below illustrate the formation of twovarieties of the fuel. It will be appreciated that steps 1-3 may all bedone concurrently, and therefore the present invention contemplates aone-step reaction that simplifies the manufacturing of the fuel therebyreducing the associated complexity and cost.

The following examples exemplify reactions in accordance with thepresent invention.

Experimental Procedure for the Synthesis of 2,3-Bis (tetrazolo) NitroBenzene.

2,3-dicyano Nitrobenzene (at about 1 g, or about 5.776 mmol), Sodiumazide (at about 0.938 g, or about 14.44 mmol) and Zinc Bromide (at about1.5133 g, or about 5.776 mmol) were mixed in 30 mL of water, and themixture allowed to reflux for 36 hrs.

The reaction cooled to room temperature, and the reaction mixture wasacidified by 3N HCl to yield a white solid. The solid was filtered, andthen dried at 105° C. As indicated below, the reaction product structurewas confirmed by IR and DSC. The reaction product exhibited relativelyhigh energy and good burn rates in excess of 0.4 inches per second, whenevaluated as known in the art.

Infrared (IR) Data indicated 1539 cm⁻¹ for ring tetrazole, 1345 cm⁻¹ forNO₂, 2600-2800 cm⁻¹ for CH₂ and 3100 cm⁻¹ for N—H stretching, therebyconfirming the reaction product structure. Differential scanningcalorimetry (DSC) evaluations indicated a sharp exotherm at 244° C.

Experimental Procedure for the Synthesis of 3,4-Bis (Tetrazolo)NitroBenzene.

3,4-dicyano Nitrobenzene (at about 1 g, or about 5.776 mmol), Sodiumazide (at about 0.938 g, or about 14.44 mmol) and Zinc Bromide (at about1.5133 g, or about 5.776 mmol) were mixed in 30 mL of water, and themixture allowed to reflux for 36 hrs.

The reaction cooled to room temperature, and the reaction mixture wasacidified by 3N HCl to yield a white solid. The solid was filtered, andthen dried at 105° C. As indicated below, the reaction product structurewas confirmed by IR and DSC. The reaction product exhibited relativelyhigh energy and good burn rates in excess of 0.4 inches per second, whenevaluated as known in the art.

Infrared (IR) data indicated 1529 cm⁻¹ for ring tetrazole, 1346 cm⁻¹ forNO₂, 2600-2800 cm⁻¹ for CH₂ and 3100 cm⁻¹ for N—H stretching.Differential scanning calorimetry (DSC) evaluations indicated a sharpmelting point at 209° C. that was followed by a relatively largeexotherm at 215° C.

Each fuel is nitrogen-rich, thereby maximizing the non-metalconstituents of the total gas generant composition.

Accordingly, the present invention includes gas generant compositionscontaining a high-energy, nitrogen-rich fuel defined as a compoundhaving the structural formula of R₃—R₁—R₂, wherein R₁ is a benzene ringwith nitro substitution, R₂ is a tetrazolyl group with a C—C bond to thebenzene ring, and R3 is a tetrazolyl group with a C—C bond to thebenzene ring. The fuel is provided at about 5-50 wt % and morepreferably at about 15-30 wt %, of the gas generant composition.

Optional secondary fuels include tetrazoles such as 5-aminotetrazole;metal salts of azoles such as potassium 5-aminotetrazole; nonmetal saltsof azoles such as diammonium salt of 5,5′-bis-1H-tetrazole: nitratesalts of azoles such as 5-aminotetrazole; nitramine derivatives ofazoles such as 5-aminotetrazole; metal salts of nitramine derivatives ofazoles such as dipotassium 5-aminotetrazole; metal salts of nitraminederivatives of azoles such as dipotassium 5-aminotetrazole; nonmetalsalts of nitramine derivatives of azoles such as monoammonium5-aminotetrazole and; guanidiness such as dicyandiamide; salts ofguanidines such as guanidine nitrate; nitro derivatives of guanidinessuch as nitroguanidine; azoamides such as azodicarbonamide; nitratesalts of azoamides such as azodicarbonamidine dinitrate; and mixturesthereof. The secondary fuel can be used within this system as co-fuelsto the primary fuel. If used, the secondary fuel when combined with theprimary fuel constitutes about 5-50 wt % of the gas generantcomposition. By itself, the secondary fuel constitutes 0-45 wt %, andmore preferably about 15-30 wt % when used.

An oxidizer component is selected from at least one exemplary oxidizerselected from basic metal nitrates, and, metal and nonmetal nitrates,chlorates, perchlorates, nitrites, oxides, and peroxides such as basiccopper (II) nitrate, strontium nitrate, potassium nitrate, potassiumnitrite, iron oxide, and copper oxide. Other oxidizers as recognized byone of ordinary skill in the art may also be employed. The oxidizer isgenerally provided at about 50-95 wt % of the gas generant composition.

Processing aids such as filmed silica, boron nitride, and graphite mayalso be employed. Accordingly, the gas generant may be safely compressedinto tablets, or slugged and then granulated. The processing aid isgenerally provided at about 0-15 wt %, and more preferably at about 0-5wt %.

Slag formers may also be provided and are selected from siliconcompounds such as elemental silicone; silicon dioxide; silicones such aspolydimethylsiloxane; silicates such as potassium silicates; naturalminerals such as talc and clay, and other known slag formers. The slagformer is typically provided at about 0-10 wt %, and more preferably atabout 0-5 wt %.

The compositions of the present invention are formed from constituentsas provided by known suppliers such as Aldrich or Fisher Chemicalcompanies. The compositions may be provided in granulated form anddry-mixed and compacted in a known manner, or otherwise mixed as knownin the art. The compositions may be employed in gas generators typicallyfound in airbag devices or occupant protection systems, or in safetybelt devices, or in gas generating systems such as a vehicle occupantprotection system, all manufactured as known in the art, or asappreciated by one of ordinary skill.

As shown in FIG. 1, an exemplary inflator or gas generating system 10incorporates a dual chamber design to tailor containing a primary gasgenerating composition 12 formed as described herein, may bemanufactured as known in the art. U.S. Pat. Nos. 6,422,601, 6,805,377,6,659,500, 6,749,219, and 6,752,421 exemplify typical airbag inflatordesigns and are each incorporated herein by reference in their entirety.

Referring now to FIG. 2, the exemplary inflator or gas generating system10 described above may also be incorporated into an airbag system 200.Airbag system 200 includes at least one airbag 202 and an inflator 10containing a gas generant composition 12 in accordance with the presentinvention, coupled to airbag 202 so as to enable fluid communicationwith an interior of the airbag. Airbag system 200 may also include (orbe in communication with) a crash event sensor 210. Crash event sensor210 includes a known crash sensor algorithm that signals actuation ofairbag system 200 via, for example, activation of airbag inflator 10 inthe event of a collision.

Referring again to FIG. 2, airbag system 200 may also be incorporatedinto a broader, more comprehensive vehicle occupant restraint system 180including additional elements such as a safety belt assembly 150. FIG. 2shows a schematic diagram of one exemplary embodiment of such arestraint system. Safety belt assembly 150 includes a safety belthousing 152 and a safety belt 100 extending from housing 152. A safetybelt retractor mechanism 154 (for example, a spring-loaded mechanism)may be coupled to an end portion of the belt. In addition, a safety beltpretensioner 156 containing gas generating/auto ignition composition 12may be coupled to belt retractor mechanism 154 to actuate the retractormechanism in the event of a collision. Typical seat belt retractormechanisms which may be used in conjunction with the safety beltembodiments of the present invention are described in U.S. Pat. Nos.5,743,480, 5,553,803, 5,667,161, 5,451,008, 4,558,832 and 4,597,546,incorporated herein by reference. Illustrative examples of typicalpretensioners with which the safety belt embodiments of the presentinvention may be combined are described in U.S. Pat. Nos. 6,505,790 and6,419,177, incorporated herein by reference.

Safety belt assembly 150 may also include (or be in communication with)a crash event sensor 158 (for example, an inertia sensor or anaccelerometer) including a known crash sensor algorithm that signalsactuation of belt pretensioner 156 via, for example, activation of apyrotechnic igniter (not shown) incorporated into the pretensioner. U.S.Pat. Nos. 6,505,790 and 6,419,177, previously incorporated herein byreference, provide illustrative examples of pretensioners actuated insuch a manner.

It should be appreciated that safety belt assembly 150, airbag system200, and more broadly, vehicle occupant protection system 180 exemplifybut do not limit gas generating systems contemplated in accordance withthe present invention.

It should further be understood that the preceding is merely a detaileddescription of various embodiments of this invention and that numerouschanges to the disclosed embodiments can be made in accordance with thedisclosure herein without departing from the scope of the invention. Thepreceding description, therefore, is not meant to limit the scope of theinvention. Rather, the scope of the invention is to be determined onlyby the appended claims and their equivalents.

1. A compound defined as consisting of the structural formula ofR₃—R₁—R₂, wherein R1 is a benzene ring with nitro substitution, R2 is atetrazolyl group with a C—C bond to the benzene ring, and R3 is atetrazolyl group with a C—C bond to the benzene ring.
 2. The compound ofclaim 1 wherein said compound is 2,3-Bis(tetrazolo)Nitro benzene.
 3. Thecompound of claim 1 wherein said compound is 3,4-Bis(tetrazolo)Nitrobenzene.
 4. A composition comprising: a first fuel defined as having thestructural formula of R₃—R₁—R₂, wherein R1 is a benzene ring with nitrosubstitution, R2 is a tetrazolyl group with a C-C bond to the benzenering, and R3 is a tetrazolyl group with a C—C bond to the benzene ring,said first fuel provided at about 5-95 weight percent; an oxidizerselected from basic metal nitrates, and, metal and nonmetal nitrates,chlorates, perchlorates, nitrites, oxides, and peroxides, said oxidizerprovided at about 5-95 weight percent.
 5. The composition of claim 4further comprising: a second fuel selected from carboxylic acids; aminoacids; tetrazoles; triazoles; guanidines; azoamides; metal and nonmetalsalts thereof; and mixtures thereof said second fuel provided at about0.1-30 percent.
 6. A gas generating system containing the compound ofclaim
 1. 7. A vehicle occupant protection system containing thecompound
 1. 8. A gas generating system containing the composition ofclaim
 4. 9. A vehicle occupant protection system containing thecomposition of claim
 4. 10. A composition containing the compound ofclaim 1 and an oxidizer.
 11. A method of forming a compound comprisingthe steps of: providing a sufficient amount of water within a reactionvessel; providing a predetermined molar amount of a dicyano Nitrobenzenecompound in the reaction vessel and mixing the contents; providing amolar amount of zinc bromide, equivalent to that of dicyanoNitrobenzene, within the reaction vessel and continuing to mix;providing a molar amount of sodium azide, about two to three hines thatof dicyano Nitrobenzene, to the reaction vessel and continuing to mix;mixing the contents of the vessel to create a solution, and refluxing;and acidifying the solution to form a compound, said compound defined ashaving the structural formula of R₃—R₁—R₂, wherein R1 is a benzene ringwith nitro substitution, R2 is a tetrazolyl group with a C—C bond to thebenzene ring, and R3 is a tetrazolyl group with a C—C bond to thebenzene ring.
 12. The compound formed by the method of claim
 11. 13. Agas generant composition containing an oxidizer and the compound formedby the method of claim
 11. 14. A gas generating system containing thecompound formed by the method of claim 11.